In filtering air, it is desirable that the unfiltered air pass slowly through the filtering material in order to maximize the filtering effect of the material. However, it is also desirable that the air be filtered as quickly as possible, so as to minimize the time needed to filter the air in a given room. A solution to these conflicting goals is to provide a large surface area for the filtering material through which the unfiltered air travels.
In a conventional filtering unit, unfiltered air is drawn through the filtering material at one end and released out the opposite end. By increasing the surface area of the filtering material, the size of the filtering filtering unit, there is a trade-off between filtering effectiveness, processing speed, and the size of the unit.
Another problem associated with conventional filtering units is that the unfiltered air passes through only one filter element. Since many filtering applications involve more than one problem, such as dust and odor, it is desirable to provide two filtering elements, each designed to resolve a particular problem. Furthermore, it is desirable that the filters be interchangeable, thus allowing a single filtering unit to be easily configured for a variety of filtering applications. Previously developed systems have not adequately addressed this problem.
Because some filtering materials react unfavorably when combined with other filtering materials, it is impossible to place both filtering materials in a single filter element. However, it is often desirable to use two reactive filtering materials, such as potassium premangenate and charcoal, in a particular filtering application. Previously developed filtering units have not provided a solution to this problem.
From a user's standpoint, it is advantageous to use replaceable filter elements in a filtering unit, so that the filtering material used therein can be quickly and inexpensively changed by the user. In connection with granulated media, such as charcoal or potassium premangenate, previous developed filter frames have used tabs to secure a filter lid to the frame. The tabs, however, are prone to deterioration after frequent use, and are thus undesirable. Previously developed filter frames for fiber or pad filtering materials have proven to be unduly expensive.
Another serious problem associated with previously developed filtering units is the lack of a effective filter media for particulates which does not adversely affect "ecology" patients, those patients with a high sensitivity to chemicals. Ecology patients cannot use traditional filtering media such as fiber filters, since individual fibers will eventually "bleed off" and adversely affect the patients' allergenic condition.
Thus, a need has arisen for a filtering unit which provides effective filtering without increasing the size of the unit. Also, a need has arisen for a filtering unit which may be adapted for use in a variety of filtering applications, using filters specifically designed to resolve individual filtering problems. Furthermore, a need has arisen for filter frames which allow the user to quickly and inexpensively replace the filtering media therein. Finally, a need has arisen for a filtering media which is effective, but not detrimental to ecology patients.